Outdoor particulate matter (PM) has been associated with increased morbidity and mortality related to cardiovascular and respiratory disease. Despite the well-established effects of outdoor pollution on cardiovascular outcomes, there have been very few studies of indoor pollution and these have mostly focused on effects of indoor biomass. It is critical to understand cardiovascular effects of indoor air as people in the United States spend the great majority (over 85%) of their time indoors and indoor air quality is modifiable at the individual level. Individuals with chronic obstructive lung disease (COPD) are a high research priority as they are susceptible to the health effects of air pollution and are at increased risk for cardiovascular morbidity and mortality. While the effects of indoor pollution related to biomass has been a recent focus of worldwide efforts to reduce the burden of COPD, there is a need to study the effects of indoor pollutants at concentrations typical of US household exposures. In the proposed study, we address unique hypotheses by leveraging the infrastructure of a recently NIEHS R01-funded air cleaner intervention trial. This parent trial provides detailed participant characterization, indoor pollutant measurements, an air purifier versus sham intervention, and respiratory outcomes measures. In the current proposal, we add intermediate outcomes that have been linked to cardiovascular morbidity, including endothelial function, blood pressure, vascular stiffness, heart rate variability, markers of systemic inflammation and coagulation. We will determine the association between in-home PM concentrations and cardiovascular outcomes and determine the effect of an air purifier intervention that reduces indoor PM on these outcomes. Addressing the hypotheses in this proposal will inform our understanding of multisystem health benefits that can result from an air purifier intervention for patients with COPD, including cardiovascular in addition to respiratory outcomes. The findings have high potential to shift our approach to COPD management by defining indoor air pollution interventions as a therapy for individuals with COPD.